1. Field of the Invention
The present invention relates in general to the control of operations which occur in a programmed sequence, and more particularly relates to a general purpose sequence controller wherein a schematic electric circuit diagram comprising a ladder network of circuit lines disposed between two vertical bud lines is changeable and simulated by a special purpose control program which is previously applied to the memory device of the controller.
2. Description of the Prior Art
In the conventional programmable sequence controller, a logic operation circuit was provided to make a logic operation of an input condition and to transmit an output corresponding to the satisfaction of the input condition to the external control units of industrial machines such as machine tools. However, since the logic operation circuit was provided with only one memory element for temporarily memorizing the result of a logic operation, a series of examine commands had to be provided and unified in the form of logical AND functions for continuously examining the input conditions therewith. In such a manner examine commands for logical OR functions were logically converted to the form of examine commands of the logical AND function. On the other hand operations being executed by the examine commands of logical AND and OR functions could be given in the form of Boolean Algebra. While somewhat satisfactory, in making an executive program for sequence control in such a manner there was the disadvantage that troublesome logic operations were required and a skillful programmer was needed for developing the programming operations.
Moreover, in the first-mentioned way above, in case a series of examine commands were performed by the combination of a plurality of examine commands, the results of the logic operation executed up until then had to be transferred for memorization in a dummy output circuit during the series of logic operations. Accordingly, the programming of the executive program was made complicated and thereby deceased the effective utilization capacity of the memory device.
Furthermore, in the second-mentioned way, in case the examine commands of logical OR functions of plural groups were connected by the examine commands of logical AND functions, then the executive program was itself made long.